C[omp]ute

From: "andrew cooke" <andrew@...>

Date: Mon, 24 Nov 2008 07:33:23 -0300 (CLST)

When I read about the news that the proton mass has been calculated from
gluon vacuum fluctuations -
http://blogs.discovermagazine.com/80beats/2008/11/21/confirmed-scientists-understand-where-mass-comes-from/
- my immediate reaction was to wonder what had happened to the problem of
renormalization (that these calculations give an answer that tends to
infinity, which is not very useful for calculating a finite mass).

I don't understand this, so am just searching round for vague ideas, but
it seems that what is happening is that the calculation is based on a
lattice of a certain size.  That puts a lower limit on the scale of the
calculations, which implies an upper limit on the momentum, losing the
divergent end.  Calculations are repeated at various scales and then the
results are extrapolated to zero grid size (which still leaves open the
question of why *that* extrapolation doesn't diverge).  This might make
more sense - http://en.wikipedia.org/wiki/Renormalization#Regularization

See also http://en.wikipedia.org/wiki/Lattice_QCD and
http://www.newscientist.com/article/dn16095-its-confirmed-matter-is-merely-vacuum-fluctuations.html

Andrew